Past exam of the materials science course of the University of Cambridge / 2016 / Paper 1 / 1 / b / Solution

Count atoms before comparing cell volumes. The molecular conventional cell has eight atoms; the metallic face-centered cubic cell has four. ThusRelative to the molecular phase,The transformation therefore produces about 22.2% contraction per atom on the stated extrapolated-volume comparison. Conversely, the molecular volume is about $28.5\%$ larger than the metallic volume; these percentages have different denominators. Compressibility would be needed to turn the extrapolated comparison into exact volumes at the transformation pressure.